1. Field of the Invention
The present invention relates to an information-recording method and an information-recording medium which make it possible to record information by being irradiated with a laser beam. In particular, the present invention relates to an information-recording method, an information-recording medium, and an information-recording apparatus which are capable of improving overwrite characteristics in the high speed recording, especially archival overwrite characteristics for overwriting information after retaining the medium in a high temperature environment for a certain period of time.
2. Description of the Related Art
In recent years, the market of read-only optical disks including, for example, DVD-ROM and DVD-Video is expanded. On the other hand, rewritable DVD's including, for example, DVD-RAM, DVD−RW, and DVD+RW are introduced into the market, and the market is expanding for backup media for computers and image-recording media with which VTR may be substituted. Further, in these several years, the demand of the market has increased for the improvement in the access speed and the transfer rate of recordable DVD's.
The phase-change recording system is adopted for recordable DVD media such as DVD-RAM and DVD−RW on which information is recordable and erasable. In the case of the phase-change recording system, the recording is basically performed such that pieces of information of “0” and “1” correspond to the crystal and the amorphous. Recorded “0” and “1” can be detected by radiating the laser beam onto the crystallized portion and the amorphous portion and effecting the reproduction based on the reflected light beam.
In order to bring about the amorphous state at a predetermined position, the heating is effected so that the temperature of the recording layer is not less than the melting point of the recording layer material by radiating a laser beam having a relatively high power. On the other hand, in order to bring about the crystalline state at a predetermined position, the heating is effected so that the temperature of the recording layer is in the vicinity of the crystallization temperature of not more than the melting point of the recording layer material by radiating a laser beam having a relatively low power. By dosing so, it is possible to reversibly change the amorphous state and the crystalline state. When the overwrite recording is performed on the ordinary recordable DVD media, the recording pulse is modulated between the recording laser power and the erasing laser power which is lower than the recording laser power to newly perform the recording while erasing the amorphous marks having been already recorded.
Optical recording media, which realize satisfactory overwrite characteristics, are known, including an optical recording medium as described, for example, in Patent Document 1 in which the overwrite recording is performed with such powers that the recording power level has a value of not more than an optimum recording power and the erasing power level has a value higher than an optimum erasing power.
A drive for the ×2 speed recording (recording speed or velocity: 8.2 m/sec, transfer rate: 22 Mbps) for DVD-RAM may be exemplified in relation to a method for optimizing the erasing power, in which the trial writing is performed for data by using information on the recording power written on a disk to determine the erasing power. In this procedure, the values of the erasing power, which exceed the threshold value of the error rate on the low power side and the high power side, are determined to set the optimum erasing power so that the optimum erasing power is just at the center of the both.
[Patent Document 1] Japanese Patent Application Laid-open No. 08-007343